1. Field of the Invention
A composition of matter and process for preparing highly basic calcium sulfonate, namely a process of manufacturing compositions containing an inorganic calcium salt and a calcium salt of an organic acid, in which the acid radical contains a sulfonic group.
2. Description of the Prior Art
Overbased calcium petroleum sulfonates are useful as additives for lubricting oils, particularly crankcase oils for internal combustion engines. These material impart detergency to lubricating oils and thus assist in keeping internal engine parts clean and reduce sludge formation in the oil. By increasing the alkaline reserve of the additive, equivalent detergency is obtained with a lower concentration of additive in the lubricating oil. Also, higher alkaline reserve neutralizes larger quantities of acidic combustion products which accumlate in the oil.
Alkaline reserve can be measured by total base number (TBN), which is the number of milligrams of potassium hydroxide equivalent to the amount of acid required to neutralize the alkaline constituents present in one gram of sample. A compound having a base number higher than can be obtained from the calcium petroleum sulfonate alone is said to be "overbased", sometimes referred to as "superbasic".
In explanation of the term "overbased calcium sulfonate", normal calcium sulfonate can be described by the formula (RSO.sub.3).sub.2 Ca where RSO.sub.3 -stands for the hydrocarbyl sulfonate radical. Since the number of hydrogen equivalents of calcium and of sulfonic acid moiety in normal calcium sulfonate is 2, the metal ratio in the normal calcium sulfonate is 1. Thus by the term "metal ratio" we mean the ratio equivalents of calcium to equivalents of sulfonic acid present in a particular mixture, e.g., in a readily filterable dispersion in the case of our mixture. When the metal ratio is greater than about 2, in a lubricating oil, the invention, when the number of equivalents of calcium is substantially greater than the number of equivalents of hydrocarbyl sulfonic moiety, then the composition is termed within our definition, as "overbased".
It is known in the sulfonate art, as exemplified by Griesinger, U.S. Pat. No. 2,402,325, Campbell et al., U.S. Pat. No. 2,485,861, and Mertes, U.S. Pat. No. 2,501,731, that a normal sulfonate or a sulfonic acid, particularly one derived from petroleum oils, can be combined with substantially more saltforming reagent or inorganic metal compound than is theoretically necessary to replace the acidic hydrogens of the acid. Essentially, the technique for obtaining such materials involves the use of a large excess of neutralizing agent or inorganic metal compound with either the normal sulfonate or sulfonic acid and water, and then dehydrating the process mass at elevated temperatures. While the exact composition of the product is not known, some researchers believe, on the basis of the Tyndall effect, that the excess metal present is due to a dispersion or colloidal suspension of the inorganic metal compound or neutralizing agent in the normal sulfonate. In any event, such compositions are known to possess a high metal content which cannot be explained in many instances by known basic salt structures. Perhaps the simplest metal content sulfonate complex which can be represented by a structural formula is: ##STR2## wherein M is a divalent metal and R is an organic radical. This sulfonate complex has a "metal ratio" of 2 (the metal ratio being, for the purpose of this specification and appended claims, the ratio of total equivalents of metal in the sulfonate complex to equivalents of sulfonic acid anion therein).
In the lubrication of internal combustion engines and other machinery, it has been found that the formation of sludge deposits is associated with the oxidation of the oil and is accelerated by various catalyst, particularly acids formed in the oil from oxidation or acids which are absorbed by the oil, e.g., from the combustion of sulphur and halogen compounds in internal combustion engines. It has also been found that if the acids are neutralized instantly, the rate of sludge formation can be greatly reduced, so that the useful life of the oil in the engine is extended far beyond that of the oil which is not protected by neutralizing agents. It has also been found that calcium carbonate is one of the most satisfactory neutralizing agents.
In order to utilize the valuable protective properties of calcium carbonate, it is necessary that it be dispersed in the oil in such a fine state of subdivision that it will not interfere with the operation of machinery in which the oil is employed as a lubricant. This necessitates that the prticle size be sufficiently small that the oil will be transparent to visible light and readily filterable through ordinary filtering media, such as filter paper. When larger particles are present in the oil, making the oil cloudy or murky, there is great danger that abrasion of bearing surfaces will result, and the coarse particles may even settle out of the oil on long standing.
A number of processes have been devised for preparing dispersions of calcium carbonate of the desirable characteristics hereinabove referred to. Most of these processes involve precipitation of the calcium carbonate from solutions of calcium salts in the presence of emsulifying agents, which act as peptizers to prevent agglomeration of the particles and coagulation of the emulsions. The most common dispersing and emulsifying agent is an oil soluble sulfonate. The calcium sulfonate employed may be prepared by the sulfonation of solvent refined lubricating oil distillate, followed by conversion of the sulfonic acids to calcium soaps. The molecular weight of the sulfonic acids was about 400 to 1000. They are preferentially oil soluble and commonly known as "mahogany" acids.
U.S. Pat. No. 3,126,340 granted to Sabol et al describes a process to prepare overbased calcium sulfonate whereby alkaline earth base, hydrocarbon solvent, 25% by volume of methanol, ammonia gas and carbon dioxide are employed to prepare calcium sulfonates with up to 300 TBN. According to that patent, CO.sub.2 and NH.sub.3 form an alkaline earth carbamate which is subsequently decomposed to the carbonate. This patent was one of the first to recognize the potential benefits of ammonia as a carbonation aid or promoter.
In U.S. Pat. No. 3,155,617, granted to Voorhees, certain water soluble organic acids are disclosed as slo-called "activators" for use in the preparation of overbased calcium sulfonates. When used in combination with other promoters, such as water or methanol, these acids, according to the patent, activate lime particles by destroying the surface carbonate coating on hydroxide molecules.
Alkyl phenols are disclosed as promoters in U.S. Pat. No. 3,172,855 granted to Noyes et al. These represent an unusual class of promoters, in that they are readily soluble in lubricating oils. Typically, most overbasing promoters are water soluble only.
In U.S. Pat. No. 3,856,687, granted to Lowe, it is disclosed that post formation additions of imidazoline polyalkoxylated compounds are desired as acid neutralizing accelerators in oils.
Prior art processes generally prevented the dispersion of crystalline carbonates during the process, by including a substantial excess of hydrated lime during processing, and by limiting the amount of carbon dioxide delivered during overbasing to between 0.4 to 0.8 mols CO.sub.2 per mole hydrated lime. Illustrative processes where the CO.sub.2 is limited to no more than 0.8 mols CO.sub.2 per mole hydrated lime include U.S. Pat. No. 3,537,996 to Hoist et al and U.S. Pat. No. 4,165,291 to Gragson.
Previously known processes for overbasing calcium petroleum sulfonates have experienced difficulty in obtaining sufficiently high alkaline reserves, e.g., TBN of 300 mg KOH/gm or higher, to enable the formulator to use lower amounts of additive while maintaining equivalent detergency or to adequately protect the engine under conditions of high acid formation in the combustion process.
In summary, a considerable variety of processes exist to prepare overbased calcium sulfonates. The majority of these processes use alcohols and particularly methanol as promoters and generally in amounts greater than 10% of the batch yield.